Index matching layers

ABSTRACT

Optical devices such as eyeglass lenses and digital displays having improved optical characteristics achieved, in part, through incorporation of an index matching system between material layers having different refractive indices.

RELATED APPLICATIONS

This application claims benefit of and priority to U.S. ProvisionalApplication Ser. No. 62/382,924 filed Sep. 2, 2016, entitled IndexMatching Layers, which is hereby incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to systems and methods for reducinginterference fringes in optical and display applications and, moreparticularly, to the incorporation of refractive index matching systemsbetween refractive mismatched layers and/or substrates.

BACKGROUND OF THE INVENTION

High refractive index ophthalmic eyeglass lenses are attractive optionsfor their increased refractive power and decreased thickness. However,the common use of low refractive index backside hard-coatings createsinterference fringes on such lenses which can strongly detract from theappearance of the lens.

Common ophthalmic lenses are made from relatively soft polymericmaterials prone to scratching. Hence, in order to provide adequatesurface robustness, lenses must be coated with a scratch resistantcoating. Such “hard-coatings” are often formed from urethane lacquers,siloxane polymers, or colloidal dispersions of oxide nano-particles,such as silicon dioxide, SiO₂. These layers are usually deposited by dipbased processes, coating both sides of the lens. A typical thickness ofthe coating is in the range of 1-5 micrometers in order to achieve thedesired abrasion resistance with high adhesion and resistance tocracking. In this range of thickness, the hard-coatings can have aneffect on the cosmetic performance of the lens. This is especially thecase when the hard-coating is not closely index matched to the lensmaterial. The reflection from an interface is given by Formula A:

$R = \left\lbrack \frac{\left( {n_{1} - n_{o}} \right)}{\left( {n_{1} + n_{o}} \right)} \right\rbrack^{2}$

Where n_(o) is the index of the incident medium (typically air) and n₁is the index of the other surface forming the interface. Consider theexample of a high index lens (n₁=1.70) and an incident medium of air(n_(o)=1). The reflection at this interface can then be calculated as6.72%. This is for a single interface; hence, a total reflection of thelens is 13.4%. This shows the importance of antireflection coatings tolower this number and increase the transmission. The most commonhard-coatings have an index of 1.5, significantly different from the1.70 lens. The reflection from the hard-coating is lower than thereflection from the lens surface. While this would initially seembeneficial (lowering the reflection), the interface between thehard-coating and the lens also generates a reflection which must also beconsidered. The different reflections are shown below in Table 1.

TABLE 1 Interface n₁ n_(o) Reflectance (%) Lens - Air 1.70 1.00 6.72Hard-Coating - Air 1.50 1.00 4.00 Lens - Hard-Coating 1.70 1.50 0.39

While the magnitude of the reflection from an interface between a 1.7(lens) and 1.5 (hard-coating) index step is much smaller than the otherreflections it has a significant impact on the reflected spectrum fromthe lens. Since light is a wave the reflections from the differentinterfaces combine destructively or constructively depending on thewavelength of light. For example, in FIG. 1, the straight line is thereflection from a single surface of a 1.67 index lens with an indexmatched hard-coating. The oscillating line is the single surfacereflection of a 1.67 index lens with a 1.5 index, mismatchedhard-coating that is 4 micrometers thick. As can be seen, the effect isvery large—varying the reflection from over 6% to almost as low as 2%.These oscillations give rise to a coloration of the lens surface. Sincetypical hard-coatings are deposited by dip processes, they are notperfectly uniform which means the reflection spectra changes over thelens surface. This, in turn, generates interference effects similar tothe fringes observed on a soap bubble and significantly detracts fromthe appearance and performance of a lens

The above example demonstrates the advantages to using index matchedhard-coatings for any given lens material. However, there are severallimitations that can prevent this from occurring. First, hard-coatingsare not available in all commercially used lens material indices. Thereis a trend towards increasing lens indices to better serve individualsrequiring high refractive powers and to allow thinner more attractivelenses. However, new lens material development is often in advance orahead of the development of hard-coatings having similar indices.Therefore, it is often the case that lens materials new to the marketplace do not have closely refractive index matched hard-coatingsavailable.

The second limitation relates to processing a lens blank into a finishedlens. When a semi-finished lens is made into a specific prescription fora patient, the back surface of the lens is ground away and polished to aspecific curve to generate the desired optical refracting power. Theremoval of material from the back surface of the lens also removes thefactory applied hard-coating. In most labs, a new or replacementbackside hard-coating is applied via spin coating and UV curing. Theavailable UV cured, spin coat, hard-coatings are mostly based onsiloxane chemistries which limits the refractive index to around 1.5.Accordingly, in the case of high index lenses, the effect describedabove occurs on the back surface of the lens. Because high indexmaterials have increased refractive power relative in comparison tocommon lens materials, such as CR39, high index lens materials are oftenemployed for prescriptions with high corrective power. However, theincreased refractive power also allows the lens thickness to bedecreased which many eyeglass wearers find attractive. Unfortunately,this desirable decrease in lens thickness is often accompanied by thedegradation in the appearance of the lens due to the index mismatchbetween the hard-coating and the lens.

Applying an antireflective, AR, coating to such a lens can make theabove-described problem worse. The oscillation in the reflectance isstill present in the reflection spectrum, albeit with a reducedamplitude. However, the amplitude of the oscillation is similar inmagnitude to the reflection from the AR coating. This can result indistortion of the color of the antireflection coating. Since thehard-coating thickness changes over the lens surface, the distortionchanges over the lens surface making it very noticeable. This effect isshown in FIGS. 2A and 2B which provide a comparison of a reflectionspectrum of a lens having an antireflection coating with an indexmatched hard-coating (FIG. 2A) versus a lens having an antireflectioncoating with a mismatched hard-coating, i.e. a 1.5 index hard-coating ona 1.67 index lens (FIG. 2B). The straight lines in FIGS. 2A and 2Brepresent the reflection from the surface of the lens without a hardcoating or an anti reflective coating applied.

A third limitation relates to the use of index matching hard-coatingsfor photochromic lenses. Photochromic lenses contain one or morephotochromic dyes in a layer on top of a lens, in a laminate embeddedinside of a lens, or dispersed within the bulk lens material. Whenexposed to a specific wavelength band of light, the dyes undergo areversible transformation between a clear, high light-transmitting stateand a darkened, reduced light-transmitting state. In ophthalmic lenses,this functionality is employed to make lenses darken when used outsidein sunlight and clear or clearer when used indoors. The wavelengths oflight responsible for this color transformation are in the UV spectrum,typically between 300 to 400 nm. This creates a potential problem whenthe photochromic functionality is combined with high indexhard-coatings.

For example, to achieve high refractive indices, commercially availablehard-coatings contain dopants such as TiO₂ or thio-urethanes. Bothmaterials are UV absorbing and reduce the amount of UV light reaching aphotochromic dye employed on or within the photochromic lens. This isshown in FIG. 3 which compares the transmission spectrum of twocommercially available hard-coatings; HC-A having a refractive indexnear 1.50 (low index) and HC-B having a refractive index near 1.67 (highindex). The reduced transmission of HC-B from 300 to 380 nm will degradethe performance of a UV activated photochromic material. To maintain theperformance, it would therefore be necessary to use a coating more likeHC-A. However, this would then lead to the same color variation anddegraded appearance as described above.

In view of the above, it becomes apparent that there is a need in thefield for a means of utilizing the available and commercially common lowindex hard-coatings with high index lenses and other optical substrateswhile minimizing the undesirable optical effects, e.g. interferencefringes, of the typical mismatched refractive indices of thehard-coating and high index optical substrates.

OBJECTS AND SUMMARY OF THE INVENTION

These objectives are achieved by the present invention, in part, byproviding an eyeglass lens having reduced interference fringescomprising a base lens substrate having a first refractive index; anindex matching system disposed on a surface of the base lens substrate;and a coating disposed on a surface of the index matching system havinga second refractive index that differs from the first refractive indexby 0.08 or greater.

In certain embodiments of the present invention: the base lens substratecomprises a high index lens material; the base lens substrate comprisesa functional film laminate; the base lens substrate comprises aphotochromic property; the index matching system is disposed on a frontand/or back surface of the base lens substrate; the index matchingsystem comprises a series of layers of materials wherein immediatelyadjacent layers of materials have distinct refractive indices relativeto one another; the index matching system comprises a series ofalternating urethane-based layers having different refractive indices;the coating is a UV cured hard-coating; the first refractive index (thelens substrate) is equal to or greater than 1.60 and the secondrefractive index (the coating) is approximately 1.50; the eyeglass lensfurther comprising an antireflective system disposed on the coating; theeyeglass lens has a single surface peak-to-peak reflectance variationwithin the visible spectrum of equal to or less than 2 percent, equal toor less than 1 percent, or equal to less than 0.5 percent; and the indexmatching system comprises a multilayered system; and combinationsthereof.

These objectives are also achieved by the present invention, in part, byproviding a system for improving optical characteristics in opticaldevices comprising a first material layer having a first refractiveindex; a second material layer having a second refractive indexdifferent from the first refractive index; and an index matching systeminterposed between the first material layer and the second materiallayer that attenuates a total reflectance of incident light of theoptical device.

In certain embodiments of the present invention: the optical device isan eyeglass lens; the optical device has a single surface peak-to-peakreflectance variation within the visible spectrum of equal to or lessthan 2 percent, equal to or less than 1 percent, or equal to less than0.5 percent; the index matching system comprises a series of layers ofmaterials wherein immediately adjacent layers of materials have distinctrefractive indices relative to one another; and combinations thereof.

These objectives are further achieved by the present invention, in part,by providing a method for reducing interference fringes observed in anoptical article comprising: obtaining a base lens substrate having afirst refractive index; forming an index matching system on a surface ofthe base lens substrate having a plurality of material layers withdifferent refractive indices relative to one another; and applying acoating on a surface of the index matching system having a secondrefractive index that differs from the first refractive index by 0.08 orgreater.

In certain embodiments of the present invention: obtaining the base lenssubstrate having the first refractive index comprises obtaining aneyeglass lens; forming the index matching system on the surface of thebase lens substrate having the plurality of material layers withdifferent refractive indices relative to one another comprises forming aseries of layers of materials wherein immediately adjacent layers ofmaterials have distinct refractive indices relative to one another; andcombinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which embodiments ofthe invention are capable of will be apparent and elucidated from thefollowing description of embodiments of the present invention, referencebeing made to the accompanying drawings, in which

FIG. 1 is a graph comparing the percent reflectance relative towavelength of a 1.67 index lens with an index matched hard-coating and a1.67 index lens with a 1.5 index, mismatched hard-coating.

FIG. 2A is a graph showing the percent reflectance relative towavelength of a lens having an antireflection coating with an indexmatched hard-coating.

FIG. 2B is a graph showing the percent reflectance relative towavelength of a lens having an antireflection coating with a mismatchedhard-coating.

FIG. 3 is a graph showing the transmission relative to wavelength of twocommercially available hard-coatings.

FIG. 4 is a cross-sectional view of a lens employing an index matchingsystem according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view of an index matching system accordingto one embodiment of the present invention.

FIG. 6 is a table showing exemplary materials used for forming an indexmatching system according to one embodiment of the present invention.

FIG. 7 is a graph showing peak-to-peak reflection variation relative tothe different refractive indices of different hard-coatings applied to abase substrate.

FIG. 8 is a cross-sectional view of a lens employing an index matchingsystem according to one embodiment of the present invention.

FIG. 9 is a table showing the configuration of an index matching systemaccording to one embodiment of the present invention.

FIG. 10 is a graph comparing reflectance relative to wavelength of alens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating; and a lens employing only an index matched lens substrateand hard-coating; and a lens employing only an index mismatched lenssubstrate and hard-coating.

FIG. 11 is a table showing the configuration of an index matching systemaccording to one embodiment of the present invention.

FIG. 12 is a graph comparing reflectance relative to wavelength of twodifferent lenses employing different index matching systems according toembodiments of the present invention and a lens employing only an indexmismatched lens substrate and hard-coating.

FIG. 13A is a photograph showing the visible fringes of an indexmismatched lens and hard-coating.

FIG. 13B is a photograph showing the visible fringes of an indexmismatched lens and hard-coating employing an index matching systemaccording to one embodiment of the present invention.

FIG. 14 is a graph comparing reflectance relative to wavelength of alens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating and an antireflective coating employed over thehard-coating and a lens employing only an index matched lens substrateand hard-coating and an antireflective coating employed over thehard-coating.

FIG. 15 is a graph comparing reflectance relative to wavelength of alens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating and an antireflective coating employed over thehard-coating and a lens employing only an index matched lens substrateand hard-coating and an antireflective coating employed over thehard-coating.

FIG. 16 is a table showing the configuration of an index matching systemaccording to one embodiment of the present invention.

FIG. 17 is a graph comparing reflectance relative to wavelength of alens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating and a lens employing only an index matched lens substrateand hard-coating.

FIG. 18 is a table showing the photochromic responses of a photochromiclens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating and the photochromic responses of various photochromiclenses not employing an index matching system according to the presentinvention.

FIG. 19 is a graph comparing reflectance relative to wavelength of aphotochromic lens employing an index matching system according to oneembodiment of the present invention between an index mismatched lenssubstrate and hard-coating and a photochromic lens not employing theinventive index matching system between an index mismatched lenssubstrate and hard-coating.

FIG. 20 is a photograph of a photochromic lens employing an indexmatching system according to one embodiment of the present inventionbetween an index mismatched lens substrate and hard-coating and aphotochromic lens not employing the inventive index matching systembetween an index mismatched lens substrate and hard-coating.

FIG. 21 is a table showing the configuration of an index matching systemaccording to one embodiment of the present invention.

FIG. 22 is a graph comparing reflectance relative to wavelength of alens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating and a lens employing only an index matched lens substrateand hard-coating.

FIG. 23 is a table showing the configuration of an index matching systemaccording to one embodiment of the present invention.

FIG. 24 is a graph comparing reflectance relative to wavelength of alens employing an index matching system according to one embodiment ofthe present invention between an index mismatched lens substrate andhard-coating and a lens employing only an index matched lens substrateand hard-coating.

DESCRIPTION OF EMBODIMENTS

Specific embodiments of the invention will now be described withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Theterminology used in the detailed description of the embodimentsillustrated in the accompanying drawings is not intended to be limitingof the invention. In the drawings, like numbers refer to like elements.

The present invention provides, in part, a means of utilizing commonlyavailable low refractive index hard-coatings with high index lenseswhile minimizing the effect of the typical mismatched indices and theaccompanying undesirable optical effects produced by the same. Thisimprovement is, in part, achieved by introducing an index matchingsystem between the hard-coating and the surface of the lens or opticalsubstrate.

In an embodiment of the present invention, with reference to FIG. 4, anophthalmic eyeglass lens 10 employs an index matching system 12 that isapplied, coated, or otherwise incorporated between a surface 18 of alens substrate 14 and a surface 20 of a hard-coating 16 that are indexmismatched. For example, the lens substrate 14 may have a refractiveindex of 1.67 and the hard-coating 16 may have a refractive index of1.50. The surface 18 of the lens substrate 14 may be a surface of thelens substrate 14 that is closest to the eye of the lens user or wearer,i.e. may be a back-lens surface, or may be a surface of the lenssubstrate 14 that is farthest from the eye of the lens user or wearer,i.e. may be a front lens surface.

In certain embodiments, as shown in FIG. 5, the ophthalmic eyeglass lens10 further employs an antireflective system 34 that is applied, coated,or otherwise incorporated directly on top of a surface 36 ofhard-coating 16. The antireflective system 34 may, for example, beformed of a series of alternating layers of high refractive indexmaterial, mid-refractive index material, and/or low refractive indexmaterial relative to one another.

The index matching system of the present invention is formed of a seriesor stack of layers of materials wherein immediately adjacent layers ofmaterials have distinct or different refractive indices relative to oneanother. For example, in certain embodiments, an index matching systemaccording to the present invention employs a first layer of a high indexmaterial, a second layer of a low index material, and a third layerformed of a same or different high index material. For example, the highindex material can be zirconium dioxide, ZrO₂, and a low index materialcan be silicon dioxide, SiO₂.

For the sake of clarity, as used herein with regard to the inventiveindex matching system and antireflective systems, the term highrefractive index or high index, means an index of refraction that isapproximately greater than about 1.9 at a referenced wavelength, forexample a wavelength of about 550 nanometers. The term low refractiveindex, or low index, means an index of refraction that is approximatelyless than about 1.55 at a referenced wavelength, for example awavelength of about 550 nanometers. The term mid-refractive index, ormid-index, means an index of refraction approximately between about 1.55and 1.9 at a referenced wavelength, for example a wavelength of about550 nanometers. Low refractive index materials may include, for example,silicon dioxide. Mid-refractive index materials may include, forexample, yttrium oxide, silicon oxynitride or aluminum oxide; and highrefractive index materials may include, for example, titanium dioxide,tantalum pentoxide, and zirconium dioxide.

In certain embodiments, the layers of the inventive index matchingsystem are formed of only high index materials; the layers of the indexmatching system are formed of only low index materials; or the layers ofthe index matching system are formed of only mid-index materials,wherein immediately adjacent layers of materials have distinct ordifferent refractive indices relative to one another.

Alternatively, in certain embodiments of the present invention, theinventive index matching system is formed of alternating layers ofurethane-based materials having distinct or different refractiveindices. For example, in certain embodiments, the urethane-basedmaterials are aqueous polyurethane dispersion primer coatings havingdistinct or different refractive indices relative to one another, forexample, refractive indices in the range of about 1.47 to 1.70. Examplematerials are described in Publication No. US 2012/0315485 A1 thecontent of which is incorporated herein in its entirety. Specificexamples of primers are PR1165 from SDC Technologies (n=1.50) and X105Efrom ITOH Optical Industrial Co (n=1.63).

FIG. 6 shows the refractive indices of exemplary materials that may beemployed in the forming the inventive index matching system and that areemployed in the below described examples.

The layer or layers of the index matching system of the presentinvention are deposited on a surface of a lens substrate or othersurface by, but not limited to, vacuum deposition (e.g. e-beam,sputtering, and/or atomic layer deposition) and/or by liquid precursors(e.g. Langmuir Blodgette, spin coating, and/or dip coating). Those ofskill in the art will understand that the index matching system of thepresent invention is suitable for deposition or implementation inprescription or Rx laboratories and/or in high-volume eyeglass lensmanufacturing facilities, depending on the deposition equipment anddeposition materials available and the skill level of the facility.

In certain embodiments of the present invention, the inventive indexmatching system is employed on non-ophthalmic applications, examples ofwhich include, but are not limited to, display systems, opticalapplications (such as non-ophthalmic lenses and components), andwindows. The common characteristic of the various applications of thepresent invention being that the application includes at least twodifferent layers of materials having distinct refractive indices.

In certain embodiments of the present invention, the inventive indexmatching system is employed on injection molded and cast molded, singleor multifocal eyeglass lenses. Such lenses may further employ otherfunctional properties such as coloration, tinting, polarization,photochromism, electrochromism, UV absorption, narrow band filtering,easy-cleaning, hydrophobicity, hydrophilicity, and anti-static. Suchfunctional properties may be imparted or incorporated into or onto suchlenses in the form of coatings, treatments, films and/or film laminates.

The index matching system of the present invention, in part,advantageously reduces a peak-to-peak reflectance variation resultingfrom the mismatch between, for example, a hard-coating and a base lensmaterial or substrate to which the hard-coating is applied. Twoillustrative examples are shown in FIG. 7. The data shows thepeak-to-peak reflection variation through the visible spectrum relativeto the different refractive indices of the different hard-coatingsapplied to a base substrate. The “Poly Lens” samples representhard-coatings of different indices applied to a polycarbonate basesubstrate having a refractive index of approximately 1.58, and “1.67Lens” samples represent the same hard-coatings applied to a basesubstrate formed of cast MR10 from Mitsui having a refractive index ofapproximately 1.67. The data represents the average peak-to-peak heightin the reflection variation due to the hard-coat to lens mismatch. Thehard-coat indices are fixed to the specific value for this example andnot true dispersion curves. For the sake of clarity, the peak-to-peakvariation is the absolute difference in reflection between adjacentpeaks and valleys in the reflection spectrum. Referencing FIG. 1, theaverage peak maximum is approximately 6.3 percent and the average peakminimum is approximately 2.2 percent. The peak-to-peak difference istherefore 4.1 percent.

It is evident from FIG. 7 that even relatively small index mismatcheswill begin inducing sizable changes in reflectance with wavelength. Thiswill then induce noticeable changes in undesirable reflected color orcolors across the optical surface of the substrate. Refractive indexdifferences of 0.03 will induce peak-to-peak reflection variations ofapproximately 1%. The index matching system of the present inventionadvantageously reduces the average peak-to-peak reflection variation ina defined wavelength band or wavelength range and, in certainembodiments, reduces the average peak-to-peak variation across thevisible. In certain embodiments of the present invention, the singlesurface peak-to-peak reflectance variation within the visible spectrumis, for example, below 2%; below 1.0% or below 0.5%.

This novel reduction in peak-to-peak reflectance variation allows theimproved use of existing hard-coatings with new high index lensmaterials; UV curable coatings with different lens materials; and lowindex hard-coatings with high index photochromic lenses in which thehard-coating and lens material are optically coupled (i.e. separated byless than 20 microns) such that interference effects are evident.

The following examples are provided to further clarify and demonstrateefficacy of the index matching system of the present invention forimproving lens system performance and should not be interpreted limitingthe scope and the manner of implementing the present invention.

Example 1

With reference to FIGS. 4 and 8-10, a Design 1 a of the inventive indexmatching system was modeled. With reference to FIGS. 8 and 9, the Design1 a employed the index matching system 12 formed of a first layer 22having a thickness of 4.2 nanometers of ZrO₂ applied directly on thesurface 18 of the lens substrate 14 (FIG. 3); a second layer 24 having athickness of 40.0 nanometers of SiO₂ applied directly on a surface 26 ofthe first layer 22; and a third layer 28 having a thickness of 6.3nanometers of ZrO₂ applied directly on a surface 30 of the second layer24. A surface 32 of the index matching system 12 is a surface upon whichthe hard-coating 16 is applied or otherwise formed.

FIG. 10 compares the modeled reflection spectra for (1) a lens employingthe above described inventive index matching system 12, Design 1 a,disposed between a 1.67 index lens substrate 14 and a 1.5 index,mismatched hard-coating 16; (2) a lens employing a 1.67 index lenssubstrate 14 with an index matched hard-coating 16 (i.e. no inventiveindex matching system 12); and (3) a lens employing a 1.67 index lenssubstrate 12 with a 1.5 index, mismatched hard-coating 16 (i.e. noinventive index matching system 12). As shown in FIG. 10, the amplitudeof the oscillation of the reflectance of the lens 10 employing the abovedescribed inventive index matching system 12 between a 1.67 index lenssubstrate 14 and a 1.5 index, mismatched hard-coating 16 (1) is greatlyreduced relative to the lens employing a 1.67 index lens substrate witha 1.5 index, mismatched hard-coating and no inventive index matchingsystem 12 (3).

Example 2

With reference to FIGS. 4, 8, 11, and 12, a Design 1 b of the inventiveindex matching system was modeled. With reference to FIG. 11, the Design1 b employed the index matching system 12 formed of a first layer 22having a thickness of 7.0 nanometers of ZrO₂ applied directly on thesurface 18 of the lens substrate 14 (FIG. 3); a second layer 24 having athickness of 50.0 nanometers of SiO₂ applied directly on a surface 26 ofthe first layer 22; and a third layer 28 having a thickness of 6.3nanometers of ZrO₂ applied directly on a surface 30 of the second layer24. A surface 32 of the index matching system 12 is a surface upon whichthe hard-coating 16 is applied or otherwise formed.

FIG. 12 compares the modeled reflection spectra for (1) a lens employingthe above described index matching system of Design 1 a, disposedbetween a 1.67 index lens substrate 14 and a 1.5 index, mismatchedhard-coating 16; (2) a lens employing the above described index matchingsystem of Design 1 b, disposed between a 1.67 index lens substrate 14and a 1.5 index, mismatched hard-coating 16; and (3) a lens employing a1.67 index lens substrate 12 with a 1.5 index, mismatched hard-coating16 (i.e. no inventive index matching system). As shown in FIG. 12, incertain embodiments of the present invention, a position or a range ofwavelengths of minimum amplitude variation of reflectance can beselectively optimized or shifted by manipulating the thickness of thevarious layers of the inventive index matching system. For example, FIG.12 shows that the lens of Design 1 a described above and shown in FIG. 9has a range of wavelengths of minimum amplitude variation of reflectancefrom approximately 425 to 450 nm. In contrast, the lens of Design 1 bdescribed above and shown in FIG. 11 has a range of wavelengths ofminimum amplitude variation of reflectance from approximately 525 to 550nm.

Accordingly, in certain embodiments of the present invention, the indexmatching system is designed to allow the edges of the spectrum of visualsensitivity (below 400 nm and above 700 nm) to have a larger variationor amplitude of reflectance since the human eye will not see the opticaleffect of this oscillation as easily. This range of wavelengths ofminimum amplitude variation of reflectance may also be optimizedaccording to the specific application of the index matching system, forexample, so as to optimize viewing of specific displays or viewing of orthrough eyeglass lenses intended for use during specific activities.

Example 3

FIGS. 13A and 13B show photographs comparing two 1.70 index lenses oneemploying the inventive index matching system (FIG. 13B) and the otherlens not employing the inventive index matching system (FIG. 13A). Bothlenses shown have a commercially available UV curable 1.5 index(approximate) backside hard-coating (for example UV-NV; Ultra Optics)applied as an outer most layer.

The benefit of the index matching system of the present invention isimmediately obvious from comparison of FIGS. 13A and 13B. In thestandard mismatched index lens and hard-coating configuration (FIG. 13A)there are many colored fringes of irregular shapes that are tightlypacked. This effect detracts from the appearance of the lens. With theinventive index matching system described above employed between thehard-coating and the lens surface (FIG. 13B), the number of fringes isgreatly reduced and are spaced much further apart, hence, significantlyimproving the appearance of the lens.

Example 4

With reference to FIGS. 14 and 15, the benefit of the inventive indexmatching system employed between the lens and mismatched hard-coating isfurther realized when the inventive index matching system is employedbetween a lens surface and an index mismatched hard-coating and anantireflective coating is further applied on top of the hard-coating. InFIG. 14, the thin line represents the reflectance of a lens having anantireflective coating applied over an index mismatched hard-coatingwithout employing the inventive index matching system between the lensand hard-coating. The thick line represents the reflectance of a lenshaving an antireflective coating applied over an index mismatchedhard-coating applied over the inventive index matching system which isapplied directly on the surface of the lens. The amplitude variationshown in FIG. 14 for a lens having an antireflective coating appliedover an index mismatched hard-coating without employing the inventiveindex matching system between the lens and hard-coating will visiblyalter the reflected color of the coating over the surface of the lens.Furthermore, since the hard-coating is non-uniform, the position of theoscillations shifts creating the appearance of color bands or fringes.When the inventive index matching system is employed, the magnitude ofthe oscillation is greatly reduced which also reduces the appearance ofthe color bands or fringes.

In certain embodiments of the index matching system of the presentinvention, the system is designed so as to minimize oscillation wherethe antireflective coating has a maximum amplitude of oscillation whileallowing some oscillation where the antireflective coating naturally hasminimum amplitude of oscillation near zero reflection. In this manner,the inventive index matching system and the antireflective system worktogether with the index mismatched hard-coating and lens combination toprovide the best possible visual appearance with minimum color bandingand maximum uniformity of appearance. This improves the aestheticappearance and performance of high index prescription lenses.

To further show the benefits of the index matching system of the presentinvention, 1.67 index lenses were prepared with and without theinventive index matching system between the lens surface and thehard-coating and then an antireflective coating was applied over thehard-coating. For the antireflective coating, a standard five-layerantireflective (AR) coating was used. The resulting spectra are shown inFIG. 15 (measured from a Filmetrics spectrometer, hence, only showing aback-lens surface reflectance). The benefit of employing the inventiveindex matching system is clearly evident through the reduced amplitudeof the oscillation of reflectance.

Example 5

In further embodiments of the index matching system of the presentinvention, a layer stack of Y₂O₃ and SiO₂ is used to form the desiredmatching coating. A mid-index coating of Y₂O₃ is a desirable materialsince the index is closer to that of common eyeglass lens materials.Additionally, both Y₂O₃ and SiO₂ are readily deposited by E-Beamevaporation which allows for control of coating stress. This helpsreduce propensity for coating cracking or crazing as layer and systemthicknesses increase. A Design 2 of the inventive index matching systemis shown in FIG. 16. For the sake of clarity, the system shown in FIG.16 is substantially similar to the system shown and described withrespect to FIGS. 4 and 8, with the exception that the inventive systemof Design 2 employs additional layers 23, 24, 28, n₁, n₂, n₃, etc.between the surface 18 of the lens substrate 14 and the hard-coating 16(FIG. 3).

The modeled reflection spectrum of the system of Design 2 disposedbetween a 1.67 index lens substrate and a 1.5 index, mismatchedhard-coating (thick line) and a lens employing a 1.67 index lenssubstrate with a 1.5 index, mismatched hard-coating without theinventive index matching system (thin line) is shown in FIG. 17. Theperformance of the inventive index matching system to reduce thevariation in the reflection spectrum is obvious and significant, e.g.below approximately 0.5% across most of the visible spectrum. This isimpressive performance for combining a 1.50 index hard-coating with a1.67 index lens, reducing the peak-to-peak variation by a factor of 7(see FIG. 7).

The index matching system Design 2 was further tested and used to coat a1.67 index lens containing a photochromic laminate embedded in the lens.Exemplary methods for formation of such high index photochromic lensesare described in the Assignee's Pub. No. US 2017/0165878 A1, the contentof which is herein incorporated by reference in its entirety.

The photochromic response was measured for lenses with (a) nohard-coating (1.67 Photo NHC); (b) with a low index 1.48 hard-coatingand no inventive index matching system (1.67 Photo No Match); (c) with a1.48 index hard-coating with the inventive index matching system ofDesign 2 (1.67 Photo with Match); (d) with a 1.60 index hard-coating andno inventive index matching system (1.67 Photo H604); and (e) with a1.67 index matched hard-coating and no inventive index matching system(1.67 Photo with Match). The luminous transmission (Y) for thephotochromic inactivated (clear) and activated transmission (darkenedstate) for these sample lenses are shown in FIG. 18.

As evident from FIG. 18, the high index hard-coatings increase theactivated transmission (Y—Activated) by approximately 5, therebydegrading the photochromic performance relative to an uncoated lens by asignificant, visually noticeable amount. This is expected due to the UVabsorption of the high index hard-coating, as shown in FIG. 7. Using alow index hard-coating the photochromic performance is recovered andimproved upon relative to the uncoated lens. This improvement is aresult of the overall increase in UV transmission into the lens with alow index hard-coating. The two low index hard-coated samples arenominally the same for activation.

FIG. 19 shows the reflection spectrum for lenses with a 1.48 indexhard-coating with the inventive index matching system of Design 2 (solidline) and for lenses with a low index 1.48 hard-coating and no inventiveindex matching system (broken line). As evident from FIG. 19, the samplenot employing the inventive coating has a peak-to-peak variation in thereflection greater than 3%. This leads to easily observable colorfringes across the lens surface. On the other hand, the sample employingthe inventive coating has a greatly reduced variation in the reflection(less than 1%). This small amplitude does not result in noticeable colorfringes, thereby, improving the appearance of the lens system. Hence,the inventive index matching system of the present invention makes itpossible to maintain and even improve upon the photochromic performancewhile maintaining the visual color band free appearance of the lens.

FIG. 20 shows photographs of a sample lens with a 1.48 indexhard-coating with the inventive index matching system of Design 2 (A)and for lenses with a low index 1.48 hard-coating and no inventive indexmatching system (B). The benefit of the index matching system of thepresent invention is immediately obvious from comparison of lenses (A)and (B). In the lens with a low index 1.48 hard-coating and no inventiveindex matching system (B) there are many fringes of irregular shapesthat are tightly packed. This effect detracts from the appearance and,hence, the value of the lens. With the inventive index matching systemdescribed above employed between the hard-coating and the lens surface(A), the number of fringes is greatly reduced, if not absent, and,hence, significantly improves the appearance and value of the lens.

Example 6

In yet another example of the index matching system of the presentinvention, a system employing alternating layers of SiO_(x)N_(y) andSiO₂ was modeled. A mid-index layer SiO_(x)N_(y) is a desirable materialsince the index is close to that of common lens materials and can becontrolled between the index of SiO₂ (1.46) and SiO₃N₄ (2.0).SiO_(x)N_(y) is readily deposited by sputtering using a silicon targetand a controlled supply of oxygen and nitrogen. This providesversatility in a coating platform—a wide range of indices from 1.46 to2.0 can be deposited from just one target. An index matching systemDesign 3 is shown in FIG. 21. For the sake of clarity, the system shownin FIG. 21 is substantially similar to the system shown and describedwith respect to FIGS. 4 and 8, with the exception that the inventivesystem of Design 3 employs additional layers 23, 24, 28, n₁, n₂, n₃,etc. between the surface 18 of the lens substrate 14 and thehard-coating 16 (FIG. 3).

The modeled reflection spectrum of the system of Design 3 disposedbetween a 1.67 index lens substrate and a 1.50 index, mismatchedhard-coating (thick line) and a lens employing a 1.67 index lenssubstrate with a 1.5 index, mismatched hard-coating without theinventive index matching system (thin line) is shown in FIG. 22. Theperformance of the inventive index matching system to reduce thevariation in the reflection spectrum is obvious and significant, e.g.below approximately 0.5% across most of the visible spectrum. This isimpressive performance for combining a 1.50 index hard-coating with a1.67 index lens, reducing the peak-to-peak variation by a factor of 7(see FIG. 7).

Example 7

In another embodiment of the index matching system of the presentinvention, a layer stack of different urethane dip coatings is employed.Such coatings are described in Publication No. US 2012/0315485 A1 thecontent of which is incorporated herein in its entirety. Such materiallayers offer the ability to vary the refractive index of the coatingfrom 1.50 to higher values. Such materials may be hard-coatings or morecommonly urethane primer layers used to improve adhesion between a lensand hard-coating. Such coatings are used in high volume manufacturingemploying dip coating processes. A Design 4 of the inventive indexmatching system is shown in FIG. 23. For the sake of clarity, the systemshown in FIG. 23 is substantially similar to the system shown anddescribed with respect to FIGS. 4 and 8, with the exception that theinventive system of Design 4 employs additional layers 23, 24, 28, n₁,n₂, n₃, etc. between the surface 18 of the lens substrate 14 and thehard-coating 16 (FIG. 3).

The modeled reflection spectrum of the system of Design 4 disposedbetween a 1.67 index lens substrate and a 1.50 index, mismatchedhard-coating (thick line) and a lens employing a 1.67 index lenssubstrate with a 1.5 index, mismatched hard-coating without theinventive index matching system (thin line) is shown in FIG. 24. Theperformance of the inventive index matching system to reduce thevariation in the reflection spectrum is obvious and significant, e.g.below approximately 0.5% across most of the visible spectrum. This isimpressive performance for combining a 1.50 index hard-coating with a1.67 index lens, reducing the peak-to-peak variation by a factor of 7(see FIG. 7).

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are proffered by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

What is claimed is:
 1. An eyeglass lens having reduced interferencefringes comprising a base lens substrate having a first refractiveindex; an index matching system disposed on a surface of the base lenssubstrate; and a coating disposed on a surface of the index matchingsystem having a second refractive index that differs from the firstrefractive index by 0.08 or greater.
 2. The eyeglass lens of claim 1wherein the base lens substrate comprises a high index lens material. 3.The eyeglass lens of claim 1 wherein the base lens substrate comprises afunctional film laminate.
 4. The eyeglass lens of claim 1 wherein thebase lens substrate comprises a photochromic property.
 5. The eyeglasslens of claim 1 wherein the index matching system is disposed on a backsurface of the base lens substrate.
 6. The eyeglass lens of claim 1wherein the index matching system comprises a series of layers ofmaterials wherein immediately adjacent layers of materials have distinctrefractive indices relative to one another.
 7. The eyeglass lens ofclaim 1 wherein the index matching system comprises a series ofalternating urethane-based layers having different refractive indices.8. The eyeglass lens of claim 1 wherein the coating is a UV curedhard-coating.
 9. The eyeglass lens of claim 1 wherein the firstrefractive index is equal to or greater than 1.60 and the secondrefractive index is approximately 1.50.
 10. The eyeglass lens of claim 1further comprising an antireflective system disposed on the coating. 11.The eyeglass lens of claim 1 wherein the eyeglass lens has a singlesurface peak-to-peak reflectance variation within the visible spectrumof equal to or less than 2 percent.
 12. The eyeglass lens of claim 1wherein the index matching system comprises a multilayered system.
 13. Asystem for improving optical characteristics in optical devicescomprising a first material layer having a first refractive index; asecond material layer having a second refractive index different fromthe first refractive index; and an index matching system interposedbetween the first material layer and the second material layer thatattenuates a total reflectance of incident light of the optical device.14. The system of claim 13 wherein the optical device is an eyeglasslens.
 15. The system of claim 13 wherein the optical device has a singlesurface peak-to-peak reflectance variation within the visible spectrumof equal to or less than 2 percent.
 16. The system of claim 13 whereinthe index matching system comprises a multilayered system.
 17. Thesystem of claim 13 wherein the index matching system comprises a seriesof layers of materials wherein immediately adjacent layers of materialshave distinct refractive indices relative to one another.
 18. A methodfor reducing interference fringes observed in an optical articlecomprising: obtaining a base lens substrate having a first refractiveindex; forming an index matching system on a surface of the base lenssubstrate having a plurality of material layers with differentrefractive indices relative to one another; and applying a coating on asurface of the index matching system having a second refractive indexthat differs from the first refractive index by 0.08 or greater.
 19. Themethod of claim 18 wherein obtaining the base lens substrate having thefirst refractive index comprises obtaining an eyeglass lens.
 20. Themethod of claim 18 wherein forming the index matching system on thesurface of the base lens substrate having the plurality of materiallayers with different refractive indices relative to one anothercomprises forming a series of layers of materials wherein immediatelyadjacent layers of materials have distinct refractive indices relativeto one another.